White water rafting emerged as a recreational activity in the 1970's, growing into the present day commercial industry. Today's industry traces its roots back to a few adventurers using military surplus bridge pontoons and rafts to access and run rivers not previously accessible to the average rafter. These military-type early rafts were equipped with frames made of two-by-six lumber, held together with carriage bolts with an attached rowing platform made of cast iron. The resultant frames were heavy and cumbersome to transport and store.
Refinements in river rafts continued, as well as design improvements. The bow and stern lift became more pronounced, and chafing strips were added to protect against frame rubbing and abrasions from the river. Further developments have included fabrics such as polyester and Kevlar™, coatings such as polyvinyl chloride (PVC) and polyurethane, leading to improved boat designs. The most common currently used white water raft design is patterned after military bridge pontoons and life rafts and adapted to river running. Said raft design consists of inflatable outer tubes with an open center.
Those early frames were later replaced with welded aluminum frames, which were a significant improvement, but still were difficult to transport and store, and expensive to build. Later, the welded frames were replaced with plumbing fittings and pipe connections adapted from railing technologies, but this still resulted in a frame that had limited strength and structure and could not be disassembled easily.
In commercial river running operations, the access point to the river can often be in a remote location. If the raft and frame are bulky and cumbersome, a great deal of expense and labor are required to transport the raft to the river. As such, it is desirable to have mainframe that is able to be easily assembled and disassembled, strong enough to withstand rafting forces, and able to be contained within a small volume and of manageable weight. The instant mainframe, comprised of frame members and connector members, provides a light weight, easily transported and assembled mainframe that is able to attach to the dorsal surface of the inflatable of a float structure, provides rigid reinforcement to the top plane of the float structure, while providing both internal and external stability under pressure to the entirety of the float structure.